From d16dab6f62084d1eee77426e0953c083ff7422d8 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Fri, 29 Apr 2022 10:40:19 -0400
Subject: [PATCH] Starts introducing a sequencer, to resolve responsibility of
 `perform`.

---
 InstructionSets/M68k/Sequence.cpp             | 30 ++++++++
 InstructionSets/M68k/Sequence.hpp             | 71 +++++++++++++++++++
 .../Clock Signal.xcodeproj/project.pbxproj    |  4 ++
 3 files changed, 105 insertions(+)
 create mode 100644 InstructionSets/M68k/Sequence.cpp
 create mode 100644 InstructionSets/M68k/Sequence.hpp

diff --git a/InstructionSets/M68k/Sequence.cpp b/InstructionSets/M68k/Sequence.cpp
new file mode 100644
index 000000000..a476be507
--- /dev/null
+++ b/InstructionSets/M68k/Sequence.cpp
@@ -0,0 +1,30 @@
+//
+//  Sequence.cpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 29/04/2022.
+//  Copyright © 2022 Thomas Harte. All rights reserved.
+//
+
+#include "Sequence.hpp"
+
+using namespace InstructionSet::M68k;
+
+template <typename EnumT, EnumT... T> struct Steps {
+	static constexpr uint16_t value = 0;
+};
+
+template <typename EnumT, EnumT F, EnumT... T> struct Steps<EnumT, F, T...> {
+	static constexpr uint16_t value = uint16_t(F) | uint16_t(Mask<EnumT, T...>::value << 3);
+};
+
+uint16_t Sequence::steps_for(Operation operation) {
+	switch(operation) {
+		// This handles a NOP, and not much else.
+		default: return 0;
+
+		case Operation::ABCD:	return Steps< Step::FetchOp1, Step::Perform, Step::StoreOp1 >::value;
+	}
+}
+
+Sequence::Sequence(Operation operation) : steps_(steps_for(operation)) {}
diff --git a/InstructionSets/M68k/Sequence.hpp b/InstructionSets/M68k/Sequence.hpp
new file mode 100644
index 000000000..b33ca0ce7
--- /dev/null
+++ b/InstructionSets/M68k/Sequence.hpp
@@ -0,0 +1,71 @@
+//
+//  Sequencer.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 29/04/2022.
+//  Copyright © 2022 Thomas Harte. All rights reserved.
+//
+
+#ifndef InstructionSets_68k_Sequencer_hpp
+#define InstructionSets_68k_Sequencer_hpp
+
+#include "Instruction.hpp"
+
+namespace InstructionSet {
+namespace M68k {
+
+/// Indicates the abstract steps necessary to perform an operation,
+/// at least as far as that's generic.
+class Sequence {
+	public:
+		Sequence(Operation);
+
+		enum class Step {
+			/// No further steps remain.
+			Done,
+			/// Fetch the value of operand 1.
+			FetchOp1,
+			/// Fetch the value of operand 2.
+			FetchOp2,
+			/// Do the logical operation.
+			Perform,
+			/// A catch-all for bus activity that doesn't fit the pattern
+			/// of fetch/stop operand 1/2, e.g. this opaquely covers almost
+			/// the entirety of MOVEM.
+			///
+			/// TODO: list all operations that contain this step,
+			/// and to cover what activity.
+			SpecificBusActivity,
+			/// Store the value of operand 1.
+			StoreOp1,
+			/// Store the value of operand 2.
+			StoreOp2,
+		};
+
+		/// @returns The next @c Step to perform, or @c Done
+		/// if no further steps remain. This step is removed from the
+		/// list of remaining steps.
+		Step pop_front() {
+			const auto step = Step(steps_ & 7);
+			steps_ >>= 3;
+			return step;
+		}
+
+		/// @returns @c true if no steps other than @c Done remain;
+		/// @c false otherwise.
+		bool empty() {
+			return !steps_;
+		}
+
+	private:
+		uint16_t steps_ = 0;
+
+		uint16_t steps_for(Operation);
+};
+
+static_assert(sizeof(Sequence) == sizeof(uint16_t));
+
+}
+}
+
+#endif /* InstructionSets_68k_Sequencer_h */
diff --git a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj
index 54f0cb863..280d5e11f 100644
--- a/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
+++ b/OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj	
@@ -1425,6 +1425,8 @@
 		4B79629D2819681F008130F9 /* Model.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = Model.hpp; sourceTree = "<group>"; };
 		4B79629E2819681F008130F9 /* Decoder.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = Decoder.hpp; sourceTree = "<group>"; };
 		4B79629F2819681F008130F9 /* Decoder.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = Decoder.cpp; sourceTree = "<group>"; };
+		4B7962A3281C1B76008130F9 /* Sequence.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = Sequence.hpp; sourceTree = "<group>"; };
+		4B7962A4281C2EE3008130F9 /* Sequence.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = Sequence.cpp; sourceTree = "<group>"; };
 		4B79A4FE1FC9082300EEDAD5 /* TypedDynamicMachine.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = TypedDynamicMachine.hpp; sourceTree = "<group>"; };
 		4B79A4FF1FC913C900EEDAD5 /* MSX.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = MSX.cpp; sourceTree = "<group>"; };
 		4B79A5001FC913C900EEDAD5 /* MSX.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = MSX.hpp; sourceTree = "<group>"; };
@@ -3161,10 +3163,12 @@
 			isa = PBXGroup;
 			children = (
 				4B79629F2819681F008130F9 /* Decoder.cpp */,
+				4B7962A4281C2EE3008130F9 /* Sequence.cpp */,
 				4B79629E2819681F008130F9 /* Decoder.hpp */,
 				4B79629C2819681F008130F9 /* Instruction.hpp */,
 				4B79629D2819681F008130F9 /* Model.hpp */,
 				4BB5B996281B1E3F00522DA9 /* Perform.hpp */,
+				4B7962A3281C1B76008130F9 /* Sequence.hpp */,
 				4BB5B997281B1F7B00522DA9 /* Status.hpp */,
 				4BB5B999281B244400522DA9 /* Implementation */,
 			);